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C-Y M-Y C-K
- To: BUG-EMACS@AI.AI.MIT.EDU
- Subject: C-Y M-Y C-K
- From: "Leigh L. Klotz" <KLOTZ@AI.AI.MIT.EDU>
- Date: Mon, 30 Mar 87 17:06:16 EST
- Cc: hal@SRI-NIC.ARPA
Hal Huntley complains that there is a bug causing recently killed
things disappear from the kill ring.
Date: Mon 30 Mar 87 10:03:01-PST
From: Hal Huntley <HAL@SRI-NIC.ARPA>
Subject: kill bug
I did the following sequence:
Move to a line and get two words from the end of the line...
Kill to end of line (C-K). ; kill 1
Add some text.
Go to next line (C-N).
Back up two words (M-B twice).
Kill to end of line (C-K). ; kill 2
Do C-Y, M-Y to get back the line I killed just above.
Back 2 words.
Kill to end of line. ; kill 3
Voila! The previous kill (kill 2) to end of line is NOT there to yank
back!!!! Not only that, but repeated M-Y's shows me that the second
kill is NOT IN THE KILL RING AT ALL!
I just reproduced this and got the same results even if I did not add
text after the first kill. Is it our NIC implementation only? I would
This needs to be fixed!
I have reproduced this now several times. I will be happy to
show anyone what I've done... (but knowing my luck when I show the
Doctor, the symptoms will go away.....)
I'm not saying that this behavior is particularly useful , but it is
consistent with the vector model of the kill ring. Interested parties can
use M-X View Q-Registerâ..K to see the kill ring and check on my
Here's how the kill vector works:
When you do C-Y, the text in kill buffer position 0 gets inserted into
When you do M-Y, that text gets deleted; the copy of the
text that was in slot 0 gets moved to slot 8, and everything else
moves down one, resulting in the previously-killed text moving from
slot 1 to slot 0; then EMACS inserts the new slot 0 text.
When you do C-K, the deleted text goes from the buffer to slot zero,
and bumps everything else up by one slot. The thing which was in slot
8 is lost.
In Huntley's example, the thing in slot 8 which gets lost is the very
thing which was in slot 0 just before the M-Y. Thus, C-Y M-Y C-K causes
the thing you C-Y'd to disappear forever.
GNU Emacs avoids this problem by keeping the kill ring in a list. If the
list length is less than the maximum kill ring length, then moving the
item to the end of the list doesn't make it a candidate for expunging on
the next kill.
TECO Emacs could emulate this behavior by skipping all Q-vector elements
containing 0 in the rotate operation, and treating the vector as if it
ended at the last non-zero element.